Neuropathic pain results from injury to a nerve. In contrast to the immediate pain (nociceptive pain) caused by tissue injury, neuropathic pain can develop days or months after a traumatic injury. Furthermore, while pain caused by tissue injury is usually limited in duration to the period of tissue repair, neuropathic pain frequently is long-lasting or chronic. Moreover, neuropathic pain can occur spontaneously or as a result of stimulation that normally is not painful.
The clinical causes of neuropathic pain are widespread and include both trauma and disease. For example, traumatic nerve compression or crush and traumatic injury to the brain or spinal cord are common causes of neuropathic pain. Furthermore, most traumatic nerve injuries also cause the formation of neuromas, in which pain occurs as a result of aberrant nerve regeneration. In addition, cancer-related neuropathic pain is caused when tumor growth painfully compresses adjacent nerves, brain or spinal cord. Neuropathic pain also is associated with diseases such as diabetes or alcoholism.
Unfortunately, neuropathic pain frequently is resistant to available drug therapies. In addition, current therapies have serious side-effects including, for example, cognitive changes, sedation, nausea and, in the case of narcotic drugs, addiction. Many patients suffering from neuropathic pain are elderly or have other medical conditions that particularly limit their tolerance of the side-effects associated with available drug therapy. The inadequacy of current therapy in relieving neuropathic pain without producing intolerable side-effects frequently is manifest in the depression and suicidal tendency of chronic pain sufferers.
Methods of alleviating neuropathic pain would improve the quality of life for many people suffering from pain due to trauma or disease. However, there currently are no effective drugs that relieve neuropathic pain without undesirable side-effects such as sedation and addiction. Thus, there is a need for methods of alleviating neuropathic pain without producing undesirable side-effects. The present invention satisfies this need and provides related advantages as well.